Failure detecting system and method for automatic transmission

ABSTRACT

A method and system for detecting a failure of an automatic transmission for a vehicle employing a speed shift range switch operation signal from a speed shift range switch as one of the control signals to control the automatic transmission. The method is carried out by: detecting a speed shift range from the speed shift range switch; generating a start signal indicating a starting state of a starter for expediting a start of an engine for the vehicle; and automatically controlling the automatic transmission so as to maintain the speed shift range in the case where &#34;P&#34; or &#34;N&#34; range is not detected when the start signal is &#34;ON&#34;.

This is a divisional of application Ser. No. 08/491,592, filed on Jun.16, 1995 which is a divisional of application Ser. No. 08/282,310, filedJul. 29, 1994 U.S. Pat. No. 5,486,147.

BACKGROUND OF THE INVENTION

The present invention relates to a failure detecting system for anautomatic transmission of a vehicle employing an engine rotationalspeed, a cruise control signal, a brake signal from a brake switch or ashift range switch operation signal from a shift range switch as one ofcontrol signals to control the automatic transmission.

An automatic transmission AT is fundamentally controlled to be shiftedby regulating depression of an accelerator pedal and a traveling speedof a vehicle. Accordingly, in case where the vehicle travels in a drive(D) range, reduction gears can be shifted by positively depressing orreleasing the accelerator pedal.

In a conventional automatic transmission, for example, in a drive (D)range, an optimum gear is selectively controlled from a vehicle speed atthat time and a throttle opening according to a shift map storing apredetermined shift schedule as shown in FIG. 14.

As a lockup function of an automatic transmission a lockup clutch isengaged when a vehicle speed becomes higher than a predetermined valuein a certain gear position such as, for example, in a third gear or anoverdrive (fourth gear), to directly couple an output shaft of a torqueconverter to an output shaft of an engine. In other cases, the lockupclutch is released to connect the input shaft of the torque converter tothe output shaft of the engine.

The lockup is released to utilize a function of the torque converterthereby to achieve smooth starting, smooth accelerating or smooth speedshifting without engine knocking or stop at the time of starting,abruptly accelerating, speed shifting the vehicle.

However, in a state that a load is low and an engine rotational speed ishigh, the torque converter is locked up thereby to prevent loss of powerdue to a slip of the torque converter and hence to prevent a decrease infuel consumption.

A cruise control unit so controls an opening of a throttle valve as tomaintain a certain vehicle speed set by a driver as a desired travelingspeed thereby controlling in response to a road state.

As the typical automatic transmission control to execute as describedabove, Japanese Utility Model Application Laid-Open 63-115558 disclosesan internal combustion engine with an abnormality detector for judgingan abnormality based on a rotational signal from a rotation detector forelectrically detecting a rotational speed of the internal combustionengine and a fuel amount signal from a fuel amount detector fordetecting a fuel supply amount to the internal combustion engine.

In the above-described internal combustion engine with the-abnormalitydetector, it is determined that an engine rotational speed signal lineis when an engine rotational speed is smaller than a predetermined valueat a certain vehicle speed or more. However, even if an engine stopoccurs at a certain vehicle speed or more, it is erroneously detectedthat the failure occurs at the engine rotational speed signal line.

In such a case, it becomes impossible to detect a failure of an ignitionpulse generating an engine rotational speed detection signal to besupplied to the engine rotational speed signal line. Furthermore, thereare disadvantages that the automatic transmission control based on theengine rotational speed such as, for example, a gear shift control, alockup control, a line pressure control can not be appropriatelycontrolled.

As the typical automatic transmission control to execute as describedabove, Japanese Utility Model Application Laid-Open 63-137038 disclosesan automatic transmission controller in which hunting of the vehiclespeed due to a gear shifting during a cruise control traveling isprevented and a fail-safe control is performed when an abnormality of anautomatic transmission occurs.

More specifically, the automatic transmission controller additionallyprovides a memory map storing a shift schedule for controlling theautomatic transmission in response to a cruise control signal suppliedfrom a cruise controller, in which map a hysteresis width is so set asto reduce the number of repetitions of down and up shifting.

In this case, since the number of times of gear shifting during thecruise control is reduced, bunching of the vehicle speed due to the gearshifting can be prevented, and a riding comfort can be improved.

In the conventional automatic transmission controller as describedabove, a vehicle can be traveled smoothly without shock in the case ofshifting gear during the cruise control, but it does not have afail-safe function in case where the cruise control signal is, forexample, erroneously generated even though the cruise control is notperformed by the cruise controller.

Usually, the automatic transmission controller functions a gear shiftingcontrol, a lockup control, an overrunning clutch control (namely, enginebrake control), etc. Therefore, if a fail-safe function is not provided,these functions are erroneously operated when a cruise control signal iserroneously generated.

In a conventional automatic transmission, for example, in a drive (D)range, an optimum gear is selected based on a vehicle speed and athrottle opening at that time, from a shift schedule map storing apredetermined shift schedule as shown in FIG. 14.

Further, in such an automatic transmission control, detection signalsfrom various detecting sensors are input to a controller to perform alockup control, an overrunning clutch control, a line pressure control,an auto-pattern select control, a gear shift timing control, a transferclutch control of four-wheel drive as well as the above-described gearshift control are executed.

Japanese Patent Application Laid-Open 1-145234 discloses a cruisecontrol of a vehicle using a brake switch signal.

More specifically, as shown in FIG. 15, a detection signal SG1 from avehicle speed sensor is input to a cruise controller 1. When a checkswitch 4 is turned on, a CPU 5 enters in an input waiting state of abrake switch signal SG2. When a brake pedal is once depressed and thenreleased, the CPU 5 decides that a series of ON/OFF signals of the brakeswitch 3 are input. In this case, a cruise control allowance flag isset, while in case the CPU 5 decides no input of the series of signals,the CPU 5 does not set the cruise control allowance flag.

Then, whether the cruise control is requested by various switches 6 forthe cruise control or not is decided. In case where the cruise controlis requested, whether the cruise control allowance flag is set or not isdecided, and in case the flag is set, the cruise control is executed.

In case where the cruise control allowance flag is not set, a warninglight is turned on to inform the gist, and cruise control is prohibited.

Thus, in such a cruise control unit for a vehicle, an error of the brakeswitch 3 is checked previously by the check switch 4 for requesting asignal check of the brake switch 3 before the cruise control. Therefore,the cruise control can be reliably executed by the brake switch 3.

However, in the above-described conventional cruise control unit for avehicle, the check switch 4 is additionally needed to check the brakeswitch 3, thereby causing a complicated structure.

Since the brake switch 3 is checked by the operation of the check switch4 only before the cruise control, there is a disadvantage that the brakeswitch 3 cannot be checked, in case where the cruise control is notexecuted. Moreover, a failure of the brake switch is not executed when abraking operation is required in various running states of the vehiclesuch as, for example, at the time of decelerating.

Further, a shift lever for operating a range shift of an automatictransmission is connected to an inhibitor switch having a plurality ofswitches corresponding to the number of operating positions. When arange is selected by the operation of the shift lever, the correspondingswitch generates a first level electric signal. Other switches notselected by the shift lever generate second level signals.

The positions of the shift lever includes, generally in the case of afour-speed automatic transmission, R (reverse), N (neutral), D (drive),3 (third), 2 (second), L (low) and P (parking) of seven positions. Theinhibitor switch for indicating the position of the shift lever includesseven switches each of which is closed (first level) when thecorresponding position of the R, N, D, 3, 2, 1, L or P is selected bythe shift lever, and opened (second level) when different positions areselected.

On the contrary, the inhibitor switch may include switches each of whichopened in the case of the corresponding shift position and closed in thecase of the different positions.

Therefore, any one of the seven switches is normally closed (opened) andthe residual six switches are opened (closed). However, if at least oneof the switches is troubled, or if an abnormality occurs at aninterlocking member for operating to open or close the switch incooperation with the shift lever, two or more switches might besimultaneously closed (opened), or all the switches might besimultaneously opened (closed). Such an abnormality causes an error inan automatic transmission control.

Switch might be, for example, instantaneously repeatedly opened/closedin an extremely short time due to a chattering when the switch ischanged from open to close or vice versa. Further, in case where amechanical member moves to sequentially close (open) one of the switchesaligned in a moving direction of the mechanical member, the adjacent twoswitches might be simultaneously closed (opened) at a certain timepoint. This is normal. However, if it is conditioned to detect as anabnormality when two or more switches are simultaneously closed or allthe switches are simultaneously opened, such a normal case as describedabove that the adjacent two switches are simultaneously closed, iserroneously determined as an abnormality.

With respect to this, Japanese Patent Application Laid-Open 63-34349discloses a method for detecting a trouble of a gear position switch.That is, if a gear position switch does not generate an ON signal when apredetermined time is elapsed after a gear shifting is performed, it isreturned to a position before the gear changing, and when the sameoperation as above is conducted predetermined times or more, the switchis decided to be a trouble.

However, in the above-described conventional method for detecting thetrouble of the gear position switch, in case where the ON signal is notgenerated from the gear position switch, the gear is returned to theposition before the gear shifting, and when the same operation as aboveis again conducted predetermined times or more, the switch is decided tobe the trouble. Therefore, in the case of the trouble, it merelycontrols to return the position Of the switch to the position before thegear shifting, an accurate automatic transmission control responsive tovarious traveling states of the vehicle is impossible.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a failure detectingsystem for an engine rotational signal line connected to a controllerfor an automatic transmission of a vehicle which can reliably detect afailure of the engine rotational signal line thereby to appropriatelycontrol an operation of an automatic transmission control based on anengine rotational speed.

In order to achieve the above object, the present invention provides afailure detecting system for engine rotational signal line of anautomatic transmission of a vehicle employing an engine rotational speedas one of control signals to control said automatic transmission, thesystem comprising:

engine speed detecting means for detecting said engine rotational speed;

air amount detecting means for detecting an amount of induction air; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said engine rotational speed, when said amount ofinduction air detected by said air amount detecting means is larger thana predetermined value, and when said engine rotational speed detected bysaid engine speed detecting means continues to be smaller than apredetermined value for more than a predetermined time.

The present invention also provides a failure detecting system for anengine rotational signal line of an automatic transmission of a vehicleemploying an engine rotational speed as one of input signals to controlsaid automatic transmission, the system comprising:

engine speed detecting means for detecting said engine rotational speed;

air amount detecting means for detecting an amount of induction air;

vehicle speed detecting means for detecting a vehicle speed; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said engine rotational speed, when said vehicle speeddetected by said vehicle speed detecting means is larger than apredetermined value, when said amount of induction air detected by saidair amount detecting means is larger than a predetermined value, andwhen said engine rotational speed detected by said engine speeddetecting means continues to be smaller than a predetermined value formore than a predetermined time.

The present invention also provides a failure detecting system for anengine rotational speed signal line connected to a controller for anautomatic transmission of a vehicle employing an engine rotational speedas one of input signals to control the automatic transmission, thesystem comprising:

engine speed detecting means for detecting said engine rotational speed;

fuel injection amount detecting means for detecting a fuel injectionamount; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said engine rotational speed, when said fuel injectionamount detected by said fuel injection amount detecting means is largerthan a predetermined value, and when said engine rotational speeddetected by said engine speed detecting means continues to be smallerthan a predetermined value for more than a predetermined time.

The present invention also provides a failure detecting system for anengine rotational signal line of an automatic transmission of a vehicleemploying an engine rotational speed as one of control signals tocontrol said automatic transmission, the system comprising:

engine speed detecting means for detecting said engine rotational speed;

vehicle speed detecting means for detecting a vehicle speed;

fuel injection amount detecting means for detecting a fuel injectionamount; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said engine rotational speed, when said vehicle speeddetected by said vehicle speed detecting means is larger than apredetermined value, when said fuel injection amount detected by saidfuel injection amount detecting means is larger than a predeterminedvalue, and when said engine rotational speed detected by said enginespeed detecting means continues to be smaller than a predetermined valuefor more than a predetermined time.

According to the failure detecting system for the engine rotationalsignal speed line of the present invention, the automatic transmissioncontrol of the automatic transmission AT is prohibited in case where oneof the following conditions is satisfied.

More specifically,

(1) When the amount of intake air is larger than a predetermined value,the state that the engine rotational speed is smaller than apredetermined value is continued for a predetermined time.

(2) When the vehicle speed is larger than a predetermined value, theamount of intake air is larger than a predetermined value and the statethat the engine rotational speed is smaller than a predetermined stateis continued for a predetermined time.

(3) When the fuel injection amount is larger than a predetermined value,the state that the engine rotational speed is smaller than apredetermined value is continued for a predetermined time.

(4) When the vehicle speed is larger than a predetermined value, thefuel injection amount is larger than a predetermined value and the statethat the engine rotational speed is smaller than a predetermined valueis continued for a predetermined time.

In case where any of the above conditions (1) to (4) is satisfied, it isdetermined that a failure occurs on the engine rotational speed signalline, whereby the automatic transmission control based on the enginerotational speed is prohibited, and the state before the failure isdetected is maintained.

Another object of the present invention is to provide a failuredetecting system for a cruise control set signal line connected to acontroller for an automatic transmission of a vehicle which can reliablydetect a failure of a cruise control set signal line thereby toappropriately control an operation of an automatic transmission controlin response to a cruise control signal.

In order to achieve the another object of the present invention, thereis provided a failure detecting system for an automatic transmission ofa vehicle employing a cruise control signal as one of input signals tocontrol said automatic transmission, the system comprising:

vehicle speed detecting means for detecting a vehicle speed;

cruise control signal generating means for generating a cruise controlsignal so as to instruct a cruise control to said automatictransmission; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said cruise control signal, when said vehicle speeddetected by said vehicle speed detecting means is smaller than apredetermined value below which said cruise control is prohibited, andwhen said cruise control signal is generated from said cruise controlsignal generating means.

The present invention also provides a failure detecting system for anautomatic transmission of a vehicle employing a cruise control signal asone of input signals to control said automatic transmission, the systemcomprising:

brake signal generating means for generating a brake signal when a brakeswitch is turned on;

cruise control signal generating means for generating a cruise controlsignal so as to instruct a cruise control to said automatictransmission; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said cruise control signal, when said brake signal isgenerated from said brake signal generating mean, and when said cruisecontrol signal is generated from said cruise control signal generatingmeans.

The present invention also provides a failure detecting system for anautomatic transmission of a vehicle employing a cruise control signal asone of control signals to control said automatic transmission, thesystem comprising:

cruise control signal generating means for generating a cruise controlsignal so as to instruct a cruise control to said automatictransmission;

shift signal generating means for generating a shift signal so as toinstruct an appropriate gear position to said automatic transmission;and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said cruise control signal, when said shift signal fromsaid shift signal generating means indicates a parking (P) or reverse(R) range, and when said cruise control signal is generated from saidcruise control signal generating means.

The present invention also provides the failure detecting system,wherein

said transmission control prohibiting means are for prohibiting atransmission control based on said cruise control signal, when saidvehicle speed detected by said vehicle speed detecting means is smallerthan a predetermined value below which said cruise control isprohibited, and when said cruise control signal is generated from saidcruise control signal generating means for a predetermined time.

According to the failure detecting system for the cruise control setsignal line of the present invention, the automatic transmission controlof the automatic transmission AT is prohibited in case where one of thefollowing conditions is satisfied.

More specifically,

(1) When the cruise control signal is erroneously turned on in casewhere a vehicle speed is smaller than a value under which the operationof a cruise control is not performed.

(2) When the cruise control signal which ought to be released iserroneously turned on at the time of turning a brake switch on.

(3) When the cruise control signal is erroneously turned on in an "N" or"P" range.

(4) When any of the paragraphs (1) to (3) is continued for apredetermined time.

In case where any of the above conditions (1) to (4) is satisfied, it isdetermined that a failure occurs on the cruise control set signal line,whereby the automatic transmission control at the time of the cruisecontrol is prohibited. However, a normal state is recovered when an offsignal of the cruise control is detected after one of theabove-described conditions is satisfied.

Still another object of the present invention is to provide a failuredetecting system for a brake switch connected to a controller for anautomatic transmission of a vehicle which can reliably detect a failureof a brake responsive to various running states thereby to appropriatelycontrol an operation of an automatic transmission control based on abrake switch signal.

The present invention also provides a failure detecting system for brakeswitch connected to a controller for an automatic transmission of avehicle employing a brake signal from a brake switch as one of inputsignals to control said automatic transmission, the system comprising:

vehicle speed detecting means for detecting a vehicle speed;

brake signal detecting means for detecting a brake signal when saidbrake switch is turned on; and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said brake signal, when a number of times of how oftensaid brake signal which ought to be detected has not been detected whilesaid vehicle is decelerated from a predetermined speed to a zero speedreaches a predetermined number of times.

The present invention also provides the failure detecting system,wherein

said transmission control prohibiting means are for prohibiting saidtransmission control based on said brake signal, when a decelerationrate of said vehicle obtained from said vehicle speed detected by saidvehicle speed detecting means, and when a number of times of how oftensaid brake signal which ought to be detected has not been detectedreaches a predetermined number of times.

The present invention also provides the failure detecting system,wherein

said transmission control prohibiting means are for prohibiting saidtransmission control based on said brake signal, when said vehicle speeddetected by said vehicle speed detecting means is larger than apredetermined speed, when a deceleration rate of said vehicle obtainedfrom said vehicle speed detected by said vehicle speed detecting meansis larger than a predetermined value, and when said brake signal whichought to be detected i not detected.

The present invention also provides a failure detecting system for abrake switch connected to a controller for an automatic transmission ofa vehicle employing a brake signal from a brake switch as one of controlsignals to control said automatic transmission, the system comprising:

brake signal detecting means for detecting a brake signal when saidbrake switch is turned on;

shift signal generating means for generating a shift signal so as toinstruct an appropriate gear position to said automatic transmission;and

transmission control prohibiting means for prohibiting a transmissioncontrol based on said brake signal, when said shift signal from saidshift signal generating means indicates a change from a parking (P)range to a reverse (R) range, and when a number of times of how oftensaid brake signal which ought to be detected has not been detectedreaches a predetermined number of times.

According to the failure detecting system for the brake switch of thepresent invention, the automatic transmission control of the automatictransmission AT is prohibited in case where one of the followingconditions is satisfied.

More specifically,

(1) When a brake ON signal is not detected when the vehicle speed isdecelerated until a vehicle is stopped, and when this phenomenon occurscontinuously predetermined times.

(2) When a deceleration of the vehicle speed is larger than apredetermined value, the brake ON signal is not detected, and when thisphenomenon occurs continuously predetermined times.

(3) In case where a vehicle speed is larger than a certain value, andthe paragraph (2) is satisfied.

(4) In a vehicle having a shift locking mechanism, when a R range isselected from a P range, absence of the brake ON signal continuouslyoccurs predetermined times.

In case where any of the above conditions (1) to (4) is satisfied, it isdetermined that a failure occurs on the brake switch signal, theautomatic transmission control in response to the brake switch signal isprohibited. However, a normal state is recovered when the brake ONsignal is detected after one of the the above-described conditions issatisfied.

Still another object of the present invention is to provide a failuredetecting system for a speed shift range switch signal line connected toa controller for an automatic transmission of a vehicle which canreliably detect a failure of a shift range switch responsive to varioustraveling states of the vehicle and can suitably conduct an operation ofan automatic transmission control based on a shift range signal.

In order to achieve the above-described object, the present inventionalso provides a failure detecting system for an automatic transmissionof a vehicle employing a shift range switch operation signal from aspeed shift range switch as one of control signals to control saidautomatic transmission, the system comprising:

vehicle speed detecting means for detecting a vehicle speed;

range detecting means for detecting a speed shift range from said speedshift range switch when a vehicle speed detected by said vehicle speeddetecting means is above a predetermined value; and

automatic transmission control means for automatically controlling saidautomatic transmission in a state that a range to be automatictransmission controlled is regarded as being a "D" range when otherspeed shift range signal is not detected even after a predetermined timeis elapsed after an "N" range is detected by said range detecting means.

The present invention also provides a failure detecting system for anautomatic transmission of a vehicle employing a speed shift range switchoperation signal from a speed shift range switch as one of controlsignals to control said automatic transmission, the system comprising:

vehicle speed detecting means for detecting a vehicle speed;

range detecting means for detecting a speed shift range from said speedshift range switch when a vehicle speed detected by said vehicle speeddetecting means is above a predetermined value; and

automatic transmission control means having display means for displayinga trouble of a "D" range when said "D" range is not detected but a "3"range is detected after an "N" range is detected by said range detectingmeans and for automatically controlling said automatic transmission soas to maintain said previously set range when a detection of said "D"range to be detected by said range detecting means is not conducted fora predetermined time.

The present invention as claimed in claim 3 provides a failure detectingsystem for an automatic transmission of a vehicle employing a speedshift range switch operation signal from a speed shift range switch asone of control signals to control said automatic transmission, thesystem comprising:

vehicle speed detecting means for detecting a vehicle speed;

range detecting means for detecting a speed shift range from said speedshift range switch signal line; and

automatic transmission control means for automatically controlling saidautomatic transmission so as to maintain said previous range when saidvehicle speed detected by said vehicle speed detecting means is above apredetermined value and when a detection of a range to be detected bysaid range detecting means is not conducted for a predetermined time.

The present invention also provides a failure detecting system for anautomatic transmission of a vehicle employing a speed shift range switchoperation signal from a speed shift range switch as one of controlsignals to control said automatic transmission, the system comprising:

range detecting means for detecting a speed shift range from said speedshift range switch;

start signal generating means for generating a start signal indicating astarting state of a starter for expediting a start of an engine for saidvehicle; and

automatic transmission control means for automatically controlling saidautomatic transmission so as to maintain said previous range in casewhere "P" or "N" range is not detected by said range detecting meanswhen a start signal from said start signal generating means is "ON".

According to the failure detecting system for the shift range switchoperation signal line of the present invention, the automatictransmission is controlled in a certain way in case where the certainconditions to determine a failure are satisfied.

More specifically,

(1) No input state is continued for a predetermined time after the "N"range is detected when the vehicle is traveled at a predeterminedvehicle speed or higher.

(2) No input state is continued for a predetermined time after the "3"range is detected in case where the "3" range is detected without thedetection of the "D" range after the "N" range is detected when thevehicle is traveled at a predetermined vehicle speed or higher.

When the condition (1) id detected, it is regarded the current shiftposition is the "D" range, the automatic gear shift control for the "D"range is conducted. When the condition (2) is detected, a failure isdisplayed, and the previous shift range is maintained.

Further,

(3) No input state of the drive range is elapsed for a predeterminedtime when the vehicle speed is a predetermined vehicle speed or higher.

(4) P or N range is not recognized when the starter switch is closed.

In case where any one of the above conditions (3) and (4) is satisfied,the range set previously is subsequently maintained.

Therefore, since the detection of the failure of the shift range switchsignal line is reliably conducted, the automatic transmission issuitably controlled by using the shift range switch operation signal.

The nature, utility, and further features of this invention will beunderstood from the following detailed description with respect topreferred embodiments of the invention by referring the accompanyingdrawings, briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing a failure detecting system for anautomatic transmission of a vehicle employing an engine rotational speedaccording to an embodiment of the present invention;

FIG. 2 is a flow chart for explaining an example of the operation of afailure detecting system for an engine rotational speed line accordingto FIG. 1;

FIG. 3 is a flow chart for explaining an example of the operation of afailure detecting system for an engine rotational speed line accordingto FIG. 1;

FIG. 4 is a flowchart for explaining an example of the operation of afailure detecting system for an engine rotational speed line accordingto FIG. 1;

FIG. 5 is a flow chart for explaining an example of the operation of afailure detecting system for an engine rotational speed line accordingto FIG. 1;

FIG. 6 is a flow chart for explaining an example of the operation of afailure detection system for a cruise control signal line according toFIG. 1;

FIG. 7 is a flow chart for explaining an example of the operation of afailure detection system for a cruise control signal line according toFIG. 1;

FIG. 8 is a flowchart for explaining an example of the operation of afailure detection system for a cruise control signal line according toFIG. 1;

FIG. 9 is a flow chart for explaining an example of the operation of afailure detection system for a cruise control signal line according toFIG. 1;

FIG. 10 is a flow chart for explaining an example of the operation ofthe failure detecting system for a brake switch according to FIG. 1;

FIG. 11 is a flow chart for explaining an example of the operation ofthe failure detecting system for a brake switch according to FIG. 1;

FIG. 12 is a flowchart for explaining an example of the operation of thefailure detecting system for a brake switch according to FIG. 1;

FIG. 13 is a flow chart for explaining an example of the operation ofthe failure detecting system for a brake switch according to FIG. 1;

FIG. 14 is a view showing a shift schedule stored in a gear shift mapfor a conventional automatic transmission control;

FIG. 15 is a view showing a conventional cruise controller;

FIG. 16 is a flow chart for explaining an example of the operation ofthe failure detecting system for a shift range switch signal lineaccording to FIG. 1;

FIG. 17 is a flow chart for explaining an example of the operation ofthe failure detecting system for a shift range switch signal lineaccording to FIG. 1;

FIG. 18 is a flowchart for explaining an example of the operation of thefailure detecting system for a shift range switch signal line accordingto FIG. 1;

FIG. 19 is a flow chart for explaining an example of the operation ofthe failure detecting system for a shift range switch signal lineaccording to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment of the present invention will be explained with referenceto accompanying drawings.

FIG. 1 shows a control system according to an embodiment of a failuredetecting system for an automatic transmission of a vehicle of thepresent invention. The control system employs an engine rotational speedas one of input signals to control the automatic transmission. A failureis detected on the engine rotational speed when conditions to bedescribed later are satisfied. When the failure is detected, atransmission control based on the engine rotational speed is prohibited,and a state before the failure is detected is maintained. The controlsbased on the engine rotational speed includes, for example, a gear shiftcontrol, a lockup control, and a line pressure control.

A throttle opening detection signal from a throttle sensor 11 and an ATFoil temperature detection signal from an ATF temperature sensor 12 areinput to an input interface circuit 21 of an electronic control unit(ECU) 20 of the control system. The throttle opening detection signalfrom the throttle sensor 11 is used to determine a gear shifting point,a line pressure in a control circuit of the automatic transmission and alockup vehicle speed for the lockup. The ATF oil temperature detectionsignal from the ATF temperature sensor 12 is used to prohibit lockup atthe time of a low temperature and to release a fourth gear.

Various detection signals input through the input interface circuit 21are converted to digital signals through an A/D converter 22, and thenfed to a CPU 24. A program for executing a predetermined calculation ofthe CPU 24 is stored in a memory 24a associated with the CPU 24.

A vehicle speed detection signal from a vehicle speed sensor 13, anengine rotational speed detection signal from an ignition pulsegenerator 14, a shift range signal from an inhibitor switch 14, and athrottle full close state detection signal from an idle switch 16, anABS signal from an ABS control unit 19a, a cruise control signal from acruise control unit, and a brake switch signal from a brake switch 19are input to an input interface circuit 23. The vehicle speed detectionsignal from the vehicle speed sensor 13 is used to control a gearshifting, lockup, line pressure and transfer. The engine rotationalspeed detection signal from the ignition pulse generator 14 is used tosmoothly control the lockup operation and to prevent overrunning of anengine in a "1", "2" or "3" range. The shift range signal from theinhibitor switch 15 is used to determine the line pressure. The throttlefull close state detection signal from the idle switch 16 is used torelease a lockup clutch and to control the line pressure.

An output of the CPU 24 is applied to an output interface circuit 25 forcontrolling ON/OFF of shift solenoids (1)31, (2)32, (3)33 and an outputinterface circuit 26 for controlling duty ratios of duty solenoids(A)34, (B)35 and (C)36.

The shift solenoids (1)31, (2)32 control gear shifting, especially, itstiming, thereby reducing a gear shifting shock. The shift solenoid (3)33controls an overrunning clutch and a timing of shifting from a thirdgear to a second gear. The timing control reduces a shock at the time ofshifting down the speed, and the overrunning clutch is operated at thetime of decelerating, thereby effecting an engine brake.

The duty solenoid (A)24 regulates the line pressure to an optimumpressure responsive to a driving state. The duty solenoid (B)35 smoothlyengages or disengages the lockup clutch. The duty solenoid (C)36regulates a hydraulic oil pressure of a transfer clutch to control therear wheel drive force.

The operation of the automatic transmission control system describedabove will be explained by referring to FIG. 2.

FIG. 2 shows a flow in case that an amount of engine intake air is usedto detect a failure of the engine rotational speed detection signal.When an air amount detection signal from an air flow sensor 17 is inputto the CPU 24 of the ECU 20, whether or not an amount of intake air islarger than a predetermined value is judged (in a step 201). When it isjudged that the amount of induction air is larger than a predeterminedvalue, whether or not an engine rotational speed based on the enginerotational detection signal from the ignition pulse generator 14 issmaller than a predetermined value is judged (in a step 202). If it isjudged that the engine speed is not smaller than a predetermined value,it is normal. A failure flag set, for example, to a register (not shown)provided in the CPU 24 is cleared, and a timer (not shown) in the CPU 24is set to a predetermined time (in steps 203 and 204).

Moreover, when it is judged that the engine rotational speed is smallerthan the predetermined value (in the step 202) and a state that theengine rotational speed is smaller than the predetermined valuecontinues for more than the predetermined time is further judged (in astep 205), a failure flag is set to the register (not shown) (in a step206). Thus, the failure flag is set to prohibit an automatictransmission control based on the engine rotational speed (in a step207), and it is controlled to maintain the previous state before theengine rotational signal failure is judged.

On the contrary, if the state that the engine rotational speed issmaller than the predetermined value continues for more than thepredetermined time is not judged (in the step 205), a failure is notdetected, and the automatic transmission based on the engine rotationalspeed is continued.

FIG. 4 shows a flow in case where the amount of intake air of a decisioncondition is replaced with a fuel injection amount. First, whether ornot the fuel injection amount is larger than a predetermined value isjudged (in a step 401). When the predetermined value of the fuelinjection amount is calculated based on the intake air amount detectionsignal from the air flow sensor 17, and compared with an actualinjection pulse width to the injection, thereby judging the fuelinjection amount. In case where it is judged that the fuel injectionamount is larger than the predetermined value, it is judged that theengine rotational speed indicated by the engine rotational detectionsignal from the ignition pulse 14 is smaller than a predetermined value(in a step 402). If it is judged that the engine rotational speed is notsmaller than the predetermined value, it is normal, a failure flag set,for example, to a register (not shown) provided in the CPU 24 is clearedand a timer (not shown) in the CPU 24 is set to a predetermined time (insteps 403 and 404).

Moreover, when it is judged that the engine rotational speed is smallerthan the predetermined value (in the step 402) and a state that theengine rotational speed is smaller than the predetermined value for morethan a predetermined time (in a step 405), a failure flat is set to theregister (not shown) (in a step 406). Thus, the failure flag is set toprohibit the automatic transmission control based on the enginerotational speed (in a step 407), and the state before the enginerotational speed failure is detected is maintained to be controlled.

On the contrary, in case where the state that the engine rotationalspeed is smaller than a predetermined value is not continued for thepredetermined time (in the step 405), it is not decided to be failure,and the automatic transmission control based on the engine rotationalspeed is continued.

In the embodiment described above, the case where the amount of intakeair and the fuel injection amount are larger than predetermined valuesis employed as one factor of the decision condition. However, thepresent invention is not limited to the particular embodiment. Forexample, as shown in FIGS. 3 and 5, a vehicle speed detected by thevehicle speed sensor 13 may be added to the decision condition.

More specifically, summary of flows of the case where theabove-described factors are employed as decision conditions is asfollows.

(1) When the amount of engine intake air is larger than a predeterminedvalue, the state that the engine rotational speed is smaller than apredetermined value is continued for a predetermined time.

(2) When the vehicle speed is larger than a predetermined value, theamount of intake air is larger than a predetermined value and the statethat the engine rotational speed is smaller than a predetermined stateis continued for a predetermined time.

(3) When the fuel injection amount is larger than a predetermined value,the state that the engine rotational speed is smaller than apredetermined value is continued for a predetermined time.

(4) When the vehicle speed is larger than a predetermined value, thefuel injection amount is larger than a predetermined value and the statethat the engine rotational speed is smaller than a predetermined valueis continued for a predetermined time.

In case where any of the above conditions (1) to (4) is satisfied, it isdetermined that a failure occurs on the engine rotational speed signal,the automatic transmission control based on the engine rotational speedis prohibited, and the state before the failure of the engine rotationalspeed signal is detected is maintained.

In the embodiment described above, in case where the amount of intakeair or the fuel injection amount is larger than predetermined value,when the engine rotational speed detection signal from the ignitionpulse generator 14 is not suitably detected, a failure is determined,and the automatic transmission control is executed in the state beforethe failure is determined. Therefore, since the failure of the enginerotational speed signal can be reliably detected, the automatictransmission control based on the engine rotational speed such as, forexample, a speed shift control, a lockup control, a line pressurecontrol can be appropriately controlled.

Another embodiment of the present invention will be explained in detailwith reference to FIGS. 6 to 9.

Referring back to FIG. 1, showing a control system including a failuredetecting system for a cruise control set signal line connected to anautomatic transmission of a vehicle. The control system employs a cruisecontrol signal from a cruise control unit as one of input signals tocontrol the automatic transmission. A failure on the cruise control setsignal line is determined when conditions to be described later aresatisfied. When the failure is detected, a transmission control based ona cruise control signal is prohibited. However, a normal state isrecovered when an OFF signal of the cruise control is detected in theconditions to be described later.

As the automatic transmission control in case where the cruise controlsignal from the cruise control unit is employed, there are a gearshifting control (control at the time of cruise control), a lockupcontrol (ordinarily a lockup control), an overrunning clutch control(namely, engine brake control), etc.

The operation of the failure detecting system for the cruise control setsignal line connected to the automatic transmission control systemdescribed above will be explained by referring to FIGS. 6 to 9.

FIG. 6 shows a flow to determine a case where a cruise control signal iserroneously turned on at a vehicle speed or less when the cruise controlis not operated. When a detection signal from the vehicle speed sensor13 is input to the CPU 24 through an input interface circuit 23, whetheror not it is smaller than a predetermined value is judged (in a step601). In case where it is judged that the detection signal is notsmaller than the predetermined value, a failure flag of the cruisecontrol signal is cleared, and a timer is set to a predetermined time(in steps 602 and 603).

On the contrary, in case where it is judged that the detection signal issmaller than the predetermined value, whether or not the cruise controlsignal is input is judged (in a step 604). In case where it is judgedthat the cruise control signal is input, a failure flag of the cruisecontrol signal is set thereby to decide a failure (in a step 605).

FIG. 7 shows a flow to determine a case where a cruise control signalwhich ought to be released when a brake switch is turned on iserroneously turned on. Whether or not the brake switch 19 is turned onis judged (in a step 701). In case where a brake ON signal from thebrake switch 19 is not input, a failure flag of the cruise controlsignal is cleared, and a timer is set to a predetermined time (steps 702and 703).

Moreover, in case where the brake ON signal from the brake switch 19 isinput, it is judged whether or not the cruise control signal is input isjudged (in a step 704), while when it is judged that the cruise controlsignal is input, a failure flag of the cruise control signal is set todecide a failure (in a step 705).

FIG. 8 shows a flow to determined a case where a cruise control signalis erroneously turned on in an "N" or "P" range. A neutral range (N) ora parking range "P" is judged based on a shift range signal from theinhibitor switch 15 (in a step 801). As a result of the judgement, incase it is judged that the shift range signal does not indicate theneutral range (N) nor the parking range (P), a failure flag of thecruise control signal is cleared, and a timer is set to a predeterminedtime (in steps 802 and 803).

On the contrary, in case where the neutral range (N) or the parkingrange (P) is detected in the step 801, whether the cruise control signalis input or not is judged (in a step 804). In case where the cruisecontrol signal is input, a failure flag of the cruise control signal isset to judge the failure (in a step 805).

FIG. 9 shows a flow to determine a case where any of when the cruisecontrol signal is erroneously turned on at a vehicle speed or less inthe case of cruise control non-operation, when the cruise control signalwhich ought to be released at the time of turning the brake switch on iserroneously turned on, and when the cruise control signal is erroneouslyturned on in an "N" or "P" range is continued for a predetermined time.First, when a detection signal from the vehicle speed sensor 13 is inputto the CPU 24 through the input interface circuit 23, it is judged thatthe detection signal is smaller than a predetermined value or not (inthe step 901). In case where the signal is judged not to be smaller thanthe predetermined value, whether or not the brake switch 19 is turned onis judge (in the step 902). In case where a brake ON signal from thebrake switch 19 is not input, the neutral range (N) or the parking range(P) is judged based on a shift range signal from the inhibitor switch 15(in the step 903).

As a result of the judgement, in case where the signal is judged not tobe the neutral range "N" nor the parking range "P", a failure flag ofthe cruise control signal is cleared, and a timer is set to apredetermined time (in steps 904 and 905).

Moreover, when the vehicle speed is not smaller than the predeterminedvalue (in the step 901), when the brake ON signal is detected (in thestep 902), or further when either of the neutral range (N) and theparking range (P) is detected (in the step 903), whether or not thecruise control signal is input is judged (in a step 906). If the cruisecontrol signal is not input, the flow is advanced to the step 904, andthe failure flag is cleared. However, in case where the cruise controlsignal is not input, whether the timer becomes "zero" or not is judged(in a step 907). That is, the "zero" of the timer means that thepredetermined time is elapsed. In case where the timer becomes "zero",the failure flag of the cruise control signal is set to decide thefailure (in a step 908).

Summary of the conditions for detecting the failure of the cruisecontrol set signal line is as follows.

(1) When the cruise control is not operated, the cruise control signalis erroneously turned on in case where a vehicle speed is smaller than apredetermined value.

(2) When a brake switch is turned on, the cruise control signal whichought to be released is erroneously turned on.

(3) When an "N" or "P" range, the cruise control signal is erroneouslyturned on.

(4) Any of the conditions (1) to (3) is continued for a predeterminedtime.

In case where any of the above conditions (1) to (4) is satisfied, afailure on the cruise control set signal line is detected, the automatictransmission control based on the cruise control signal is prohibited.

In the embodiment described above, a normal state is recovered when anOFF signal of the cruise control is detected after one of theabove-described conditions is satisfied.

Accordingly, since a failure of the cruise control set signal line isreliably detected, the automatic transmission control using the cruisecontrol signal is appropriately executed.

Still another embodiment of the present invention will be explained indetail with reference to FIGS. 10 to 14.

Referring back to FIG. 1, showing a control system including a failuredetecting system for a brake switch connected to an automatictransmission of a vehicle. The control system employs a brake signalfrom the brake switch as one of input signals to control the automatictransmission. A failure of the brake switch is detected when conditionsto be described later are satisfied. When the failure is detected, atransmission control based on the brake signal is prohibited. However, anormal state is recovered when an OFF signal of the cruise control isdetected after one of the conditions to be described later is satisfied.Control for a four-wheel drive transfer clutch in the automatictransmission (control at the time of operating ABS) is performed inresponse to the brake signal.

The operation of the failure detecting system for the brake switchconnected to the automatic transmission control system described abovewill be explained by referring to FIGS. 10-12.

FIG. 10 shows a flow to determined a case where a brake on signal is notdetected which the vehicle speed is decelerated until a vehicle isstopped, and when this phenomenon is continuously repeated predeterminedtimes.

More specifically, when a detection signal from the vehicle speed sensor13 is input to the CPU 24 through an input interface circuit 23, thevehicle speed is judged (in a step 1001). When the vehicle speed is, forexample, faster than 30 km/hr, a check flag is set (in a step 1002).

On the contrary, in case where the vehicle speed is slower than 30km/hr, presence/absence of the check flag is judged (in a step 1003). Ifthe check flag is not set, the check flag is reset. In case where thecheck flag is set, ON/OFF of the brake switch 19 is judged (in a step1004). If the brake switch 19 is judged to be turned on, the check flagis cleared, and a counter is also cleared (in a step 1005).

In case where the brake switch 19 is turned off, whether or not thevehicle speed becomes "zero" is judged (in a step 1006). If it is judgedthat the vehicle speed becomes "zero", the check flag is cleared, and acounter is counted up (in a step 1007). In case where a counted-up valuereaches a predetermined value N by repeating the count-up of the counter(in a step 1008), an error flag is set, and the automatic transmissionat the time of brake is prohibited (in steps 1009 and 1010).

FIG. 11 shows a flow to determine a case where the brake ON signal isnot detected when a deceleration of the vehicle is larger than apredetermined value, and when this phenomena occurs continuouslypredetermined times.

More specifically, whether the deceleration of the vehicle is largerthan the predetermined value or not is judged (in a step 1101). In casewhere it is judged that the deceleration is larger than thepredetermined value, presence/absence of the brake ON signal is judged(in a step 1102). If the brake ON signal is detected, a counter iscleared (in a step 1103).

In case where the brake ON signal is not detected, the counter iscounted up in a step 1104. When the counted-up value reaches apredetermined times, an error flag is set, and the automatictransmission control at the time of the brake is prohibited (in steps1105 to 1107).

FIG. 12 shows a flow combining both two cases described above. Whetherthe vehicle speed is faster than a predetermined value or not is judgedprior to the decision of the deceleration shown in FIG. 11 (in a step1201).

FIG. 13 shows a flow to determine a case where absence of the brake ONsignal is detected, predetermined times when the P or R range isselected in the vehicle having a shift locking mechanism.

More specifically, when a shift range signal from the inhibitor switch15 is input to the CPU 24 through the input interface circuit 23, arange position is judged (in a step 1301). In case where the range isaltered from the P range to the R range, whether or not the brake switch19 is turned on is judged (in a step 1302). That is, in this case, it ispremise that the shift locking mechanism between the P and R ranges isprovided, which is released by manipulating a shift lever with thedepression of a brake pedal.

In case where the brake ON signal is detected, stored information in aRAM(A) (not shown) of a memory 24a associated with the CPU 24 is cleared(in a step 2303). Moreover, in case where the brake ON signal is notdetected, the number of counts stored in RAM(A), indicating the numberof detections of the brake ON signal is added (in a step 1304). When theadded number in the RAM(A) reaches a predetermined value N, a brakefailure flag is set, and hence an automatic transmission control inresponse to the brake switch is prohibited (in a step 1313).

Furthermore, in case where the added number in the RAM(A) (in a step1305) does not reach the predetermined value N, the vehicle speed isjudged (in a step 1306). That is, when a detection signal from thevehicle speed sensor 13 is input to the CPU 24 through an inputinterface circuit 23, a predetermined speed is compared with a detectedspeed from the vehicle speed sensor 13, and whether the detected speedis faster than the predetermined speed or not can be judged. In casewhere it is judged that the detected speed is larger than thepredetermined speed, ON/OFF of the brake switch 19 is judged (in a step1308). In case where the brake ON signal is detected, stored informationin a RAM(B) (not shown) of the memory 24a is cleared, and further abrake failure flag is cleared (in steps 1309 and 1310).

On the contrary, in case where the brake ON signal is not detected, thenumber of counts stored in RAM(B) indicating the number of detections ofthe brake ON signal is added to the RAM(B) (in a step 1311). When theadded number in the RAM(B) reaches a predetermined value N, the brakefailure flag is set, and hence the automatic transmission control inresponse to the brake switch is prohibited (in a step 1313).

More specifically, summary of the flow detecting a failure of the brakesignal is as follows.

(1) When the vehicle speed is decelerated until a vehicle is stopped, abrake ON signal is not detected, and when this phenomenon occurscontinuously predetermined times.

(2) When a deceleration of the vehicle is larger than a predeterminedvalue, the brake ON signal is not detected, and when this phenomenonoccurs-continuously predetermined times.

(3) In case where the vehicle speed is larger than a certain value, andthe condition (2) is satisfied,

(4) In a vehicle having a shift locking mechanism, when a R range isselected from a P range, absence of the brake ON signal continuouslyoccurs predetermined times.

In case where any of the above conditions (1) to (4) is satisfied, afailure of the brake signal is detected, the automatic transmissioncontrol using the brake signal is prohibited. However, a normal state isrecovered when the brake signal is detected after one of theabove-described conditions is satisfied.

Therefore, since the check switch for instructing a check before thecruise control like prior art is eliminated, its structure is not onlysimplified, but also a failure of the brake switch in the variousrunning states is reliably detected, and hence the automatictransmission control using the brake signal is appropriately executed.

Still another embodiment of the present invention will be explained indetail with reference to FIGS. 16 to 19.

Referring back to FIG. 1, showing a control system including a failuredetecting system for a shift range (inhibitor) switch signal used for anautomatic transmission control. The control system employs a shift rangesignal from an inhibitor switch as one of control signals to control theautomatic transmission. A failure is detected when conditions of therange signal to be described later are satisfied. When the failure isdetected, a transmission control based on the range signal isprohibited.

The operation of the failure detecting system for the shift range switchsignal of the automatic transmission control system described above willbe explained by referring to FIG. 16.

First, whether the vehicle speed V is higher than a predetermined valueVo or not is judged (in a step 1601). When the vehicle speed is higherthan the predetermined value, the shift range signal from the inhibitorswitch 15 is fetched to the CPU 24 through the input interface circuit23 (in a step 1602).

Then, whether the shift range signal is input or not is judged (in astep 1603). In case where no input is judged, whether the range detectedin previous routine is the "N" range or not is judged in next step (in astep 1604). In case where the "N" range is judged, i.e., when no shiftrange signal has been input after the "N" range, lapse of a time countedby a timer is judged (in a step 1605). In case where it is judged that apredetermined time is elapsed after the step 1604 is affirmed, a failureflag is set (in a step 1606), the present range is regarded as being the"D" range, and an automatic transmission control for the "D" range isexecuted (in step 1607).

On the other hand, in case where it is judged that the shift rangesignal is present in the step 1603, the timer is set to To (in a step1608), and the input shift range signal is stored as a present range (ina step 1609).

In case where the predetermined time is not elapsed in the step 1605,the timer is counted down (in a step 1610).

FIG. 17 shows a flow of detecting a failure when a certain range isoverlooked.

First, whether the vehicle speed is a predetermined value Vo or more isjudged (in a step 1701). When the vehicle speed is higher than thepredetermined value, a shift range signal from the inhibitor switch 15is fetched to the CPU 24 through the input interface circuit 23 (in astep 1702).

Then, whether the shift range signal is input or not is judged (in astep 1703). In case where it is judged that the shift range signal isinput, the input signal range is recognized as being the present range(in a step 1704). In case where it is judged that the shift range signalis not input, whether the range detected in previous routine is the "N"range or not is judged (in a step 1705). In case where the "N" range isjudged, a check flag is set (in a step 1706). In case where the range inprevious routine is not the "N" range, whether the present shift rangeis "D" range is judged (in the step 1706). When "D" range is judged, thecheck flag is cleared (in a step 1707).

In case where the range detected in previous routine is "N" range,whether the present range is a "3" range or not is judged (in a step1708).

In case where the present range is judged to be the "3" range, a checkflag F₁ is set (in a step 1709). This check flag is set only when the"3" range is detected without the detection of "D" range immediatelyafter the "N" range. In a step 1710, the check flag F₁ is judged. Whenthe check flag is set, whether the range signal is input or not isjudged (in a step 1711). In case where it is judged that the rangesignal is absent, whether the timer is "0" or not is judged. In casewhere a predetermined time To is not elapsed, the timer is counted down(in steps 1712 and 1715). In case where it is judged that the timer is"0", an error flag is set to indicate a failure of the shift rangesignal (in a step 1713).

In case that the check flag F₁ is not set or the shift range signal ispresent, the timer is set to the predetermined time To (in a step 1714).

To summarize of the respective flows in FIGS. 16 and 17, the conditionsfor detecting the failure of the shift range switch is as follows.

(1) No input state is continued for a predetermined time after the "N"range is detected when the vehicle is traveled at a predeterminedvehicle speed or higher.

(2) No input state is continued for a predetermined time after thecertain range such as the "3" range is detected in case where such thecertain range is detected over the "D" range after the "N" range isdetected without the detection of the "D" range after the "N" range isdetected when the vehicle is traveled at a predetermined vehicle speedor higher.

In case where any one condition of the above conditions (1) and (2) issatisfied, the gear shift control is conducted. In the case of the abovecondition (1), it is regarded as being the "D" range, the gear shiftcontrol for the "D" range is conducted. In the case of the abovecondition (2), a trouble is displayed, and the gear shift control forsuch the certain range is maintained.

Therefore, since the failure of the shift range switch is reliablydetected by the foregoing logic, the automatic gear shift controlresponsive to the shift range switch is suitably conducted withoutnecessity of new failure detecting sensor.

FIGS. 18 and 19 show still another example of the condition to detectthe failure of the shift range switch.

First, in case where a shift range signal from the inhibitor switch 15is not fetched to the CPU 24 through the input interface circuit 23, thevehicle speed detection signal indicative of the vehicle speed from thevehicle speed sensor 13 and presence/absence of the shift range signalare judged (in steps 1801 and 1802).

In case where the vehicle speed is the predetermined vehicle speed ormore and the input shift range signal is present, the timer is set to apredetermined time To (in a step 1805). Then, the input shift rangesignal is stored as R_(OLD) and the gear shift control for the shiftrange indicated by the input shift range signal is performed (9n a step1806). In case where the shift range signal is not present, lapse of thetime counted by the timer is judged (in a step 1803). In case where thepredetermined time To is not elapsed, the timer is counted down (in astep 1807). In case where the predetermined time To is elapsed, theshift range operated before the shift range signal becomes absent ismaintained (in a step 1804).

In FIG. 19, in case where the "P" or "N" range is not recognized fromthe shift range signal from the inhibitor switch 15 when the starterswitch is closed, the previous shift range is maintained (in steps 1901,1902 and 1903).

On the other hand, when the starter switch is not closed in the step1901, whether the vehicle speed is faster than the predetermined vehiclespeed or not is judged. In case where the vehicle speed is faster thanthe predetermined vehicle speed, the present input of the shift rangesignal is judged (in steps 1904 and 1905). In case where it is judgedthat the shift range signal is not input at present, lapse of the timeis judged (in a step 1906). In case where the predetermined time iselapsed after the step 1905 is affirmed, the shift range operated beforethe shift range signal becomes absent (in a step 1903).

To summarize the flows in FIGS. 18 and 19, the conditions for detectingthe failure of the shift range switch is as below.

(3) No input state of the shift range at a predetermined vehicle speedor higher is elapsed for a predetermined time.

(4) P or N range is not recognized when the starter switch is closed.

In case where any one of the above conditions (3) and (4) is satisfied,the shift range used before the failure occurs is subsequentlymaintained, and the automatic gear shift control for such the maintainedshift range is suitably conducted.

While the presently preferred embodiments of the present invention havebeen shown and described, it is to be understood that these disclosuresare for the purpose of illustration and that various changes andmodifications may be made without departing from the scope of theinvention as set forth in the appended claims.

What is claimed is:
 1. A failure detecting system for an automatictransmission of a vehicle employing a speed shift range switch operationsignal from a speed shift range switch as one of control signals tocontrol said automatic transmission, the system comprising:rangedetecting means for detecting a speed shift range from said speed shiftrange switch; start signal generating means for generating a startsignal indicating a starting state of a starter for expediting a startof an engine for said vehicle; and automatic transmission control meansfor automatically controlling said automatic transmission so as tomaintain said speed shift range in case where "P" or "N" range is notdetected by said range detecting means when a start signal from saidstart signal generating means is "ON".
 2. A method for detecting afailure of an automatic transmission for a vehicle employing a speedshift range switch operation signal from a speed shift range switch asone of control signals to control said automatic transmission,comprising the steps:detecting a speed shift range from said speed shiftrange switch; generating a start signal indicating a starting state of astarter for expediting a start of an engine for said vehicle; andautomatically controlling said automatic transmission so as to maintainsaid speed shift range in case where "P" or "N" range is not detected bysaid range detecting means when a start signal from said start signalgenerating means is "ON".